In the normal operation of fixed bed chemical and oil refining reactors, the top of the catalyst bed often becomes fouled or plugged by the deposition of organometallic compounds, polymeric and carbonaceous materials and organic and inorganic particulates. The plugging of the catalyst bed is undesirable since the resultant increase in pressure drop necessitates costly shutdowns or throughput reduction and requires time consuming repairs and maintenance.
In an effort to overcome this problem, many schemes have been devised, where each reactor is equipped with more than one catalyst bed and a plugged bed is bypassed to extend the operating life of the reactor (see for example, U.S. Pat. Nos. 3,509,043; 4,313,908; and 5,670,116). The shortcoming of such teachings is that they require an auxiliary bypassable bed. For example, the above teachings are not applicable to reactors having only a single fixed bed of catalyst particles.
Additionally, schemes involving the use of what is commonly referred to in the art as trash baskets have been developed. In such schemes, as taught by U.S. Pat. Nos. 3,992,282 and 3,888,633, particulate impurities are removed from a fluid stream flowing into a fixed bed of catalyst by a hollow basket or scale traps that extends into the catalyst bed.
While the trash baskets described by the prior art tend to remove particulates contained in the fluid streams being passed through the reactor, they have only a small effect in minimizing pressure drop buildup due to fouling. The trash basket walls, usually made from screen mesh material, get fouled and plugged with particulates within a short period of time. Thus, the flow passage of the fluid streams is occluded and the pressure drop begins to rise, though at a somewhat slower rate than if the baskets were not used. Very often, it is desirable to keep these reactors on stream without significant pressure drop buildup for a long period of time lasting several years. Thus, the trash baskets do not provide adequate protection against pressure drop buildup, and an alternate method is needed to extend the run length of these reactors. What is needed in the art is a method which allows accumulation of the foulant particulates at the bed top while at the same time bypasses the reactants across this foulant particulate layer and distributes them to the catalyst bed underneath without significant pressure drop.